Great! You can tweak our art and XML (CC-by-SA license),
help with balance and contribute factions.
If you want to tweak the tech-tree itself or factions we have, then we'd love you to use github to do so - simply fork us - and then put in pull-request so we can take a look and bring your changes into our project!
If you want to contribute a new faction, then we'd love you to use github to do so - simply create your faction in a branch (with a root folder the name of your faction, e.g. /plutonians) and tell us about it in the Glest Forum, and we can link to your faction using git submodule!